'Zoobiquity': What Humans Can Learn From Animal Illness

Barbara Natterson-Horowitz is a cardiac consultant for the Los Angeles Zoo, a member of the zoo's Medical Advisory Board and director of imaging at the UCLA Cardiac Arrhythmia Center.

Joanna Brooks
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Originally published on April 24, 2013 10:05 am

Dr. Barbara Natterson-Horowitz, a cardiologist at the UCLA Medical Center, coined the term "zoobiquity" to describe the idea of looking to animals and the doctors who care for them to better understand human health. Veterinary medicine had not been on her radar at all until about 10 years ago. That's when she was asked to join the medical advisory board for the Los Angeles Zoo and she began hearing about "congestive heart failure in a gorilla or leukemia in a rhinoceros or breast cancer in a tiger or a lion."

Natterson-Horowitz explores the connection between human and veterinary medicine in a book she co-authored with Kathryn Bowers, Zoobiquity: The Astonishing Connection Between Human and Animal Health. "This comparative way of thinking is something that veterinarians learn from their first week of veterinary school," she tells Fresh Air's Terry Gross. "When they learn about the heart, they learn about a four-chambered heart in a mammal and a three-chambered heart in a reptile and a two-chambered heart in a fish. ... Physicians, we don't learn that way. We don't think that way."

The realization that a comparative approach, she says, could advance our knowledge of human medicine was something of a revelation. "It's been exciting for me," she says. " ... On rounds with students, when we're talking about ... breast cancer — to point out that breast cancer has been seen in mammals from kangaroos and camels to whales, and that there is an increased rate of breast cancer and ovarian cancer in some Venezuelan jaguars."

Doctors, she says, can also learn about human psychological issues — everything from self-injury to sexual dysfunction — from studying the same problems in animals.

"Some dogs will just lick and lick and lick at their paws until the skin breaks," she says, "and it starts to bleed, but they continue to lick. So, you see, these grooming-related behaviors ... they're presumably doing this to comfort themselves. It's a kind of attempt to take a very challenging life or environment and make it more acceptable to them."

Interview Highlights

On the fight-or-flight response

"I learned from veterinarians that, you know, animals from Rottweilers and chihuahuas, in different kinds of canaries and lap dogs, that they can also faint in response to fear, and why that happens is really interesting and shared with us. It turns out that whether it's rabbits or monkeys or deer, that danger and noise — the perception of danger — causes these animals' heart rates to plummet — particularly the juveniles — and that really superslow heart rate keeps them still, and that's probably protective. It's an anti-predation response, which is different from what we typically think about the fight or flight, so it turns out that animals and humans are equipped not with two, but with three responses: fight, flight or faint."

On a salve for self-injury among horses

"They found that ... a flank-biting stallion, if you bring that isolated horse in a stall and return it to a herd — you know, horses being herd animals — that the companionship can really improve the self-injuring behavior. If there aren't other horses, they have actually had success putting little chickens in a stall with a horse, so just the presence of companionship can help with self-injury."

On the sexual education of stallions

"How a stallion is raised from foalhood has a big impact on his sexual performance and sexual health as an adult. ... First of all, they make sure that the horse does not have too much sexual experience too early. That can be detrimental. They are careful with which mares they put with the young stallion for his first experiences. You know, a mean mare — a mare that might physically hurt the young stallion — could impact him psychologically, so they're just careful about those early sexual experiences."

On the lack of of comparative medicine education in medical school

"It used to be different. My father is a physician, and he tells me that when he went to medical school they had courses in comparative anatomy and comparative pathology, but my dad is turning 90 this year, so it seems that sometime between when he went to medical school and when I went to medical school, the comparative perspective of those courses were dropped from the curriculum."

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross.

If you're interested in animals, animal health or your own health, I think you'll be interested in the work of my guest, Dr. Barbara Natterson-Horowitz. She's a cardiologist at the UCLA Medical Center, which is a leading heart transplant hospital, where she says she's seen every type of human heart failure.

But some of what she's learned about the human heart she's learned from animals. Some of those animals live nearby at the Los Angeles Zoo, where she's called on from time to time to consult and serves on the medical advisory board. Dr. Natterson-Horowitz is also a psychiatrist, and she's gotten insights from animals about psychological problems that afflict some animals, as well as people, like obsessive-compulsive disorder, eating disorders and self-mutilation.

She and her coauthor coined the term "Zoobiquity" to describe looking to animals and veterinarians to better understand human health. Their book "Zoobiquity" has just been published in paperback. It discusses animal-human health connections in conditions ranging from stress-induced heart attacks to diabetes, cancer and sexually transmitted diseases.

Dr. Barbara Natterson-Horowitz, welcome to FRESH AIR.

BARBARA NATTERSON-HOROWITZ: Thanks for having me.

GROSS: Now, when I opened your book, I thought, oh, I'm not going to like this book, because you describe being called in for a consult at the Los Angeles Zoo to help with an emperor tamarind - which is a very small monkey - that was in heart failure.

And you're saying in this book so to establish a bond with the animal, you stare deep into her eyes as you would a child who you were treating and to establish a trust bond with the animal and put her at ease and to let her know that you understand her vulnerability and will work hard to help her.

And I thought, oh, please. Stop trying to convince me what a sensitive doctor you are. But just at that moment, just as I'm thinking that, you describe a veterinarian doctor walking into the examining room, and saying what to you?

NATTERSON-HOROWITZ: Well, yes, I was trying to do with this tamarind monkey what I would do with a human patient and kind of get close and make eye contact. And at that point, the veterinarian put his hand on my shoulder and said: Please stop making eye contact with her like that. Back up, you're scaring her, and you're going to give her capture myopathy, which was a diagnosis I had never heard before.

So I did what I was told, of course. I, you know, backed away. And, anyway, when I ended up going home, I ended up looking up capture myopathy, and I learned that there was this syndrome that veterinarians had described and had been treating and preventing for decades in which animals who were really scared, their bodies would flood with adrenaline, and that adrenaline would poison the muscles of their body, including their heart muscle, and they could sometimes die.

I had never heard of capture myopathy before, but that - the description of that diagnosis really reminded me of and resonated with a quote-unquote "human diagnosis," which had been newly identified, which was something called the broken heart syndrome, or stress cardiomyopathy.

And this disorder involves human beings, who, you know, have witnessed a horribly traumatic event, someone being killed. It has happened in people who have been left at the altar, people who have lost their life savings, you know, at the roulette table.

And what was particularly exciting and kind of my ah-ha moment, what made this an ah-ha moment for me was that this syndrome, newly present in the human literature, toward the end of, you know, around 1995 to the year 2000, but it had been in the veterinarian literature for many, many decades.

GROSS: So just to back up a second, the reason why staring into this little monkey's eyes risked giving this monkey, basically, heart failure because of capture myopathy was that staring into an animal's eyes, from the animal's point of view, means that you're threatening the animal, that you're trying to stare them down and prove that you're superior, and then maybe you'll want to attack them or even eat them...

NATTERSON-HOROWITZ: Right.

GROSS: ...which is not the message you were trying to convey. So - and that sent - that risked sending stress through the animal's body and damaging muscles, including, most importantly, the heart muscle. So once you made that connection and had that ah-ha moment, that this is happening in animals, and we've just realized, you know, through science, that this happens in humans, too, that there's a certain kind of, you know - like extreme stress reaction that can cause heart failure.

So you had this ah-ha moment. And what did that lead to in terms of you trying to understand what vets know about animals?

NATTERSON-HOROWITZ: Yeah. Well, I mean, 10 years ago when this started, I was happily practicing cardiology, you know, at UCLA. I was, you know, seeing heart attacks and atrial fibrillation and, you know, people with high cholesterol and all that. And I really had not given - I mean, veterinary medicine wasn't on my radar at all.

And then I asked to join the medical advisory board of our local zoo, at the L.A. Zoo, and it was through that that I began hearing, you know, veterinarians on rounds talking about congestive heart failure in the gorilla or leukemia in a rhinoceros or breast cancer in a tiger or lion.

And that was really the first time that I had thought much about the - you know, the diseases that I'd been taking care of in human patients for, you know, over 20 years, veterinarians were taking care of in their patients. And that experience led me to just join forces with Kathryn Bowers, the science journalist, to begin exploring what might happen if human medicine looked at key human, quote-unquote, "human" medical problems through the lens of veterinary and evolutionary biology.

GROSS: So I want to ask you to give another example of heart failure issues in animals and in people that you learned about, probably at about the same time as the capture myopathy. So you were working at the UCLA Medical Center - I forget what year this was - when was a big earthquake. And, you know, there were a lot of, like, cardiac patients you had to deal with then. And you learned from the coroner's office that in the 24 hours after the earthquake, there were four times as many cardiac deaths as typical.

And it seemed as if people were being scared to death by the earthquake. And then soon after, a wildlife vet showed you a video that made you think about those cardiovascular events after the earthquake. I want you to describe the video.

NATTERSON-HOROWITZ: Yeah. There is this phenomenon where, you know, our - you know, human beings, our nervous systems, the part of the nervous system called the autonomic nervous system - which is responsible for fight and flight and the other side, the rest and digest - it can be very activated by fear. And the earthquake in L.A. back in 1994, the Northridge Earthquake, did trigger some events in human patients. And, by the way, terrorist attacks have done the same thing.

But I was comparing notes with a wildlife veterinarian, and we were talking about this phenomenon of fear affecting the autonomic nervous systems of our patients. And he showed me a video of these shorebirds that were being netted, cannon-netted, and they needed some medical attention.

And, you know, he explained to me that occasionally, some of these shorebirds, that the shock of the noise was enough to actually trigger, you know, in some instances, a stunning and an occasional instance of actual death. So it really helped me to connect the nervous systems of these animals in humans.

And the other really interesting connection that it helped me make was, you know, why we faint sometimes in response to something really scary, like having our blood drawn or - it reminded me of the feeling that I got when I was watching that basketball game where Kevin Ware broke his leg, and just that picture induced in my own nervous system, even as a physician, this kind of woozy feeling.

And I learned from veterinarians that, you know, animals - from Rottweilers Chihuahuas to, you know, all kinds of canaries and lap dogs - that they can also faint in response to fear. And why that happens is really interesting, and shared with us. It turns out that it is, you know, whether it's rabbits or monkeys or dear, that danger and noise, the perception of danger causes these animals' heart rates to plummet, particularly the juveniles. And that really super-slow heart rate keeps them still.

And that's probably protective. It's an anti-predation response, which is different from what we typically think about, the fight or flight. So it turns out that animals and humans are equipped not with two - not just with fight or flight - but with three responses: fight, flight or faint.

GROSS: Why is this, like, an issue for cardiologists? Do you see a lot of people who have fainted?

NATTERSON-HOROWITZ: Yeah, it's a big problem. I mean, people think cardiologists only deal with heart attacks and, you know, big dramatic things, but fainting is a major issue that we deal with. About 6 percent of so of all hospital admissions are for a fainting or a fainting-related condition, and about a third or a little over a third of all adults have actually fainted at least once in their life.

GROSS: So getting back to the horrible basketball injury that you and so many others witnessed on television, how would fainting have helped you?

NATTERSON-HOROWITZ: Well, it's an interesting question, and the answer takes us into the world of evolutionary biology, which is, of course, where we end up when we start making comparisons between human and animal physiology and disease. So this super-slowing of the heart rate that is associated with this emotionally triggered fainting, it is that same slowing of the heart rate that we see in animals as we look leftward on the evolutionary timeline.

We see it in other primates, in other mammals. We see it in reptiles. We even see it in fish. And if you think about an underwater predator and an underwater prey fish, you can imagine how there might be a protective benefit from slowing your heart down very, very much when a predator is tracking you.

Many underwater predators - including some rays and some sharks - have heartbeat detectors. They're called ampullary organs, and they track the electrical impulses that come off of the heart. Some other predators can actually hear the closing of the heart valves, the bum-bum, bum-bum, bum-bum noise that your cardiologist listens to when she's listening to your heart.

So you can imagine that if a predator is tracking the prey using those signals coming off from the beacon that is that prey fish's heart, that slowing the heart dramatically from a bum-bum, bum-bum, bum-bum, bum-bum to a bum-bum, bum-bum, that that could possibly cause the predator to lose track of the animal.

It's a little bit like if you've ever seen a submarine movie, the captain of the sub that's being tracked by the other sub tells the crew to, you know, run silent, and engines are turned off, and hopefully the other submarine loses track of him and goes off.

GROSS: So one of the issues that you try to address in the book is, like, does the animal world have anything to tell us about the kind of cutting and self-injury that a lot of people are prone to - I suppose particularly teenagers. And this led you to a theory that there are forms of self-injury in the animal world that are considered to be examples of grooming gone wild. So what are some examples of that in the animal world?

NATTERSON-HOROWITZ: If you look at self-injury in a human patient, it can be really perplexing and hard to understand. But many people, many psychiatrists have commented that patients who self-injure - particularly patients who cut themselves - you ask them why they do it, and they say, well, it gives me a kind of a release, or a relief. It's soothing to them.

And that does feel very counterintuitive. But as you look at self-injury in animals, it becomes clearer why humans may self-injure, because animal self-injury typically involves a normal grooming behavior that gets amplified.

Grooming is used very frequently across the animal kingdom to soothe - animals soothe themselves. Of course, grooming also serves a function of helping to keep the animal clean, and it can be involved in bonding. But it also is a way that animals soothe themselves.

And so when you look at the typical kinds of animal self-injury, feather-plucking disorder - this is where certain birds will pluck out their feathers. Sometimes they can actually denude their bodies with this syndrome. Or stallions who are flank-biters, and some dogs will just lick and lick and lick at their paw until the skin breaks and it starts to bleed. But they continue to lick.

So you sort of see these kind of grooming-related behaviors that have just been turned up, and they're presumably doing this to comfort themselves. So it's a kind of attempt to take, you know, a very challenging life or environment and to make it more acceptable to them.

GROSS: OK. So a lot of this self-injury in animals is related to, you know, grooming gone wild. But you say some of it is also related to boredom. Animals get bored?

NATTERSON-HOROWITZ: Yeah. It's interesting that, you know, when a psychiatrist deals with a patient with self-injury, we're going to try to begin with talk therapy and develop a relationship in that way. But veterinarians who are encountering a self-injuring animal patient obviously don't have language. You know, the talking cure is not available to veterinarians. So they do something really interesting to me as a psychiatrist. They look at the environment.

And they look for specific - a couple of specific elements of the environment that are associated with self-injury. One of them is boredom. And what they've noticed, for example, if you take a stallion horse, and you strap on the feed bag, and then the horse just chows down his meal in five minutes, well, then, you know, that's a horse who's going to be bored and could get into some issues.

So what they do is they try to enrich the environment. They make it harder for the animal to access the food. They create these foraging kind of games. They make it harder to find food. It takes more time. It's intellectually challenging, perhaps, for the animal, and that's to really counter boredom, which is associated with self-injury.

Of course, they other thing that they know triggers self-injury is isolation, which is really intriguing to think about, again, in the human animal patient. They will - they found, for example, a flank-biting stallion, if you bring that isolated horse in a stall and return it to a herd - you know, horses being herd animals - that the companionship can really improve the self-injuring behavior.

If there aren't other horses, they have actually had success putting little chickens in a stall with a horse. So just the presence of companionship can help with self-injury.

GROSS: If you're just joining us, my guest is Dr. Barbara Natterson-Horowitz. She's a cardiologist, but she also consults at the Los Angeles Zoo on cardiac patients. And this got - kind of got her thinking about the comparisons between animal medicine and human medicine, and she's coauthored the book "Zoobiquity: The Astonishing Connection Between Human and Animal Health."

So another connection between animal and human medicine that you write about has to do with restraints. And doctors sometimes put hospitalized patients in restraints so that they don't pull out their IV tubes, or so that they don't, like, forget where they are and, like, walk out of bed even though they can't walk, or they shouldn't be walking.

And so you've had to do that on the cardiac unit with some patients. So what got you thinking about restraints and the connection between human and animal medicine?

NATTERSON-HOROWITZ: Well, during this period, I was in the CCU, and some patient was restrained, and I started wondering about restraint in animals. And I learned from veterinarians an interesting fact, that restraining animals can sometimes trigger this super-slowing of the heart rate, that in some instances can actually lead to fainting, and that that super-slowing of the heart rate triggered by restraint is probably an anti-predation thing.

It's - potentially, you know, leads to the animal kind of playing dead or in some way evading, you know, that - the final predatory end.

GROSS: But if they're playing dead, another animal wouldn't eat them?

NATTERSON-HOROWITZ: Yeah, it's an interesting thing. There are these fascinating examples that naturalists have described of predators, you know, not being interested in animals that they think are dead. You know, why that is, you know, it could be that they - I mean, it's a health concern. But it definitely does work some of the time for prey animals to be very, very still, and in some instances, actually, they can, you know, evade death by playing dead.

GROSS: Has this connection affected whether you put patients in restraints nowadays?

NATTERSON-HOROWITZ: I wouldn't say, really. It's more a way of thinking about these things. When I'm teaching medical students now, I try to bring in the comparative perspective, in other words talking about other animals. So it hasn't directly affected how I take care of my patients, but more how I think about my patients.

And, you know, this comparative way of thinking is something that veterinarians learn from, you know, their first week of veterinary school. They - when they learn about the heart, they learn about, you know, a four-chambered heart in a mammal and a three-chambered heart in a reptile and a two-chambered heart in a fish, and they learn about the diseases in that comparative way.

And physicians, we don't learn that way. We don't think that way. It used to be different. My father is a physician, and he tells me that he went to medical school, they had courses in comparative anatomy and comparative pathology. But my dad is turning 90 this year. So it seems that sometime between when he went to medical school and when I went to medical school, the comparative perspective of those courses were dropped from the curriculum.

And as a result, it's been exciting for me to - you know, on rounds with students when we're talking about, gosh, breast cancer - to point out that breast cancer has been seen in mammals, from kangaroos and camels to whales, and that there is an increased rate of breast cancer and ovarian cancer in some Venezuelan jaguars, and so on and so forth. So I'm kind of bringing this perspective to the bedside pretty frequently.

GROSS: Dr. Barbara Natterson-Horowitz will be back in the second half of the show. She's a cardiologist at the UCLA Medical Center and serves on the medical advisory board of the Los Angeles Zoo. Her book "Zoobiquity" has just been published in paperback. I'm Terry Gross, and this is FRESH AIR.

(SOUNDBITE OF MUSIC)

GROSS: This is FRESH AIR. I'm Terry Gross. Let's get back to our interview about what we can learn about human health from animals and the doctors who treat them, or zoobiquity, as my guest calls it. Dr. Barbara Natterson-Horowitz is a cardiologist at the UCLA Medical Center and she's on the medical advisory board of the Los Angeles Zoo. She says studying animal health has changed the way she practices medicine and the way that she teaches. She's a professor at the UCLA School of Medicine. Her book "Zoobiquity" has just come out in paperback.

So I think one of the biggest surprises I had reading your book had to do with human behavior, and that is that you were actually assigned when you were in medical school, you were assigned to watch hardcore pornography and I thought: really.

(LAUGHTER)

GROSS: So tell us about why you are assigned that.

NATTERSON-HOROWITZ: Well, I'm going to reveal how old I am. But yes, I went through my medical training before the Internet, and back then, let's say that medical students might be on the nerdy side and a little bit underexposed. So we had one course on human sexuality and one small part of that course involved briefly looking at, you know, sort of the spectrum of human sexual activity - which, you know, for a group of sort of the nerdy scientist types who were in their early 20s, it was eye-opening at the time. I think nowadays medical students have probably seen it all on the Internet long before they go to college.

GROSS: So what was the point of making sure you'd seen hardcore pornography?

NATTERSON-HOROWITZ: Well, I think really the idea is that a medical student, a physician should not express surprise or even, you know, disgust or some judgment when a patient - a vulnerable patient - is coming to them with a sexual concern, and I think that was the intention. What was interesting, as we were thinking about sexuality in animals - as Kathryn and I were writing the book - was how comfortable veterinarians are talking about the sex, the sex lives of their patients, and how often they refer to an animal breeding as a sign of good health. It's a different level of comfort, let's say, talking about their patients' sexuality.

GROSS: So one of the things that you did in trying to understand is there anything the animal world can teach us about sexuality, and so you went to a horse barn to watch handler tease the mares, which means what?

NATTERSON-HOROWITZ: Right. We went to a stallion breeding farm and we were watching a stallion breeding, which is really a sight to behold. I have to say for a city slicker like myself it was pretty eye-opening. But one of the things that we've learned, which is quite calmly explained to us, is that not every day is a good day for a stallion to be an excellent breeder, that some days it's just not going to work out. And the breeding facility where we were, they actually have something called a three mount rule, which means the horse has three chances to mount the phantom, which is what they use to collect the semen. And if it works, that's great and if it doesn't work, the horse goes back to its stall for the evening and there'll be another day where there'll be an opportunity. The veterinarians there also explained to us that how a stallion is raised from full hood has a big impact on his sexual performance and sexual health as an adult.

GROSS: What things come into play?

NATTERSON-HOROWITZ: Well, first of all, they make sure that the horse doesn't have too much sexual experience too early. That can be detrimental. They are careful with which mares they put the young stallion for his first experiences. You know, a mean mare - a mare that might physically hurt the young stallion - could impact him psychologically, so they're just careful about those early sexual experiences.

GROSS: So if a horse mounts three times and still can't get the job done, does that mean the horse has low T?

(LAUGHTER)

NATTERSON-HOROWITZ: The point was, they're just very accepting of it. You know, people think of stallions as being these big tough breeding animals but they're sensitive like we are, as humans, and the human animals, we're not machines. Things can vary, the environment can vary, hormonal levels can vary. It's of true female animals as well and we learned so much. I mean I just got such an education about sexuality in animals and female animals and like the range of desire and acceptance of sexual activity varies among females of many species. So the answer is, I think it's a normal thing. Veterinarians accept that what we would consider sexual dysfunction is a normal part of sexual function in animals.

GROSS: So how has this helped you as a cardiologist and psychiatrist?

NATTERSON-HOROWITZ: One of the most eye-opening sort of obvious - non-obvious - thing that I learned was how much non-procreative sex happens in the animal world. I guess before I hadn't given it much thought. I assume that humans we have sex, yeah, to also have babies but also, you know, to bond and for pleasure and for all kinds of reasons. But then in my mind I thought, well, animals have sex to procreate. But learning how common, gosh, all kinds of certainly same-same sexual activity has been extremely well documented in many, many species and other non-procreative activities - like self-stimulation, very, very common across species, it really sort of broadened my understanding of sort of why sexuality is important to human beings and also to the idea that pleasure plays a role in the sexuality of animals other than human beings.

GROSS: You know, one of the questions you ask in your book trying to see what you can learn about human sexuality from animal sexuality is like, do animals masturbate? And I thought oh, yeah, good question. And then you point out that like if a dog humps your leg, that's what the dog is doing.

(LAUGHTER)

GROSS: And I thought, you know, I never really quite thought of it that way. I don't know what I was thinking, maybe that my, I thought my leg was another dog or...

NATTERSON-HOROWITZ: Yeah.

GROSS: I don't know what I was thinking but that's so obviously true.

NATTERSON-HOROWITZ: Yeah. And it's funny. Your experience of like, oh yeah, that's obvious, that happened for Kathryn and me over and over and over again. I mean why wouldn't animals self-stimulate, when you think about it? And then, of course, the sexuality chapter is called "Roar-gasm." And when you think about it why wouldn't animals have an orgasm? It's just one of those things that I just had never thought about. The issue of animal masturbation is fascinating to think about, why they might be doing it, when they do it and we - the veterinary literature has so many interesting little pearls. And we found one article that tracked the time of day that bulls on certain farms masturbated. And it turned up at 5:00 a.m. was a favorite time for some of these bulls.

(LAUGHTER)

GROSS: That's interesting. I have no idea what it says, but...

(LAUGHTER)

GROSS: If you're just joining us, my guest is Dr. Barbara Natterson-Horowitz, she's the co-author of the new book "Zoobiquity: The Astonishing Connection Between Human and Animal Health." The book has actually just been published in paperback. And she is a cardiologist at the UCLA Medical Center. She's a professor at UCLA and also is a consultant to the Los Angeles Zoo.

As a psychiatrist and cardiologist, one of the issues you're interested in is, you know, the connection between depression and heart disease. And you've look to the animal world to see if there's any connection that has been found in the animal world. What did you learn?

NATTERSON-HOROWITZ: You know, it's a really good question and it's a hard question to answer because we wanted to approach all these issues from a very skeptical position. We did ask the question, can animals get mental illness? And I think it's pretty well established at this point that yes, in fact, they can. I mean there's certainly dog and cat diagnoses of separation anxiety. We know that certain breeds of dogs are susceptible to obsessive compulsive disorder. There is something called canine cognitive dysfunction, which appears to be a corollary of human Alzheimer's disease. So at this point I think we can say that mental illness does happen in animals.

The question of depression and then - in its extreme form - the question of suicidality comes up, people ask us that question. And you know, to take the question of suicidality, it's interesting to ask: Well, would an animal ever take their own life?

There are instances in which, you know, anecdotally, naturalists have written about animals becoming very sad and stopping their eating and just kind of fading away. What we know for sure, though, is that if you expand your definition of suicide from sort of the most iconic forms of human suicide - you know, a depressed patient jumping off a bridge or shooting themselves or whatever - and you think, well, suicide in humans can also include a suicide bomber, could be Jim Jones and in the jungles of Guyana having people, you know, drink cyanide. I mean, there are many forms of suicide in humans.

And if you expand the definition, then in fact I think the answer is yes, there are examples of some animals who commit suicide, particularly among insects; that is pretty well documented. There are crickets, for example, and when they're infected by a specific parasite, this worm induces changes in the cricket's central nervous system that cause the cricket to walk toward the edge of a body of water and the crickets can't swim, and the cricket literally jumps into the water and the cricket starts to, you know, flounder and drown. But as the cricket is drowning and dying, actually you can see in these videos the worm, the parasite actually coming out of the cricket's body and it needs to complete its life cycle in the water. So, in fact, infection by this parasite induces suicidal behavior in this cricket.

GROSS: So among the things that you do is that you are a professor of cardiology. So when you're talking to your students and you're making comparisons between human and animal medicine, do they really appreciate that you're involved in this area or do they think you're a little kind of outside the zone?

NATTERSON-HOROWITZ: Yeah. You know, I had already been on the faculty at UCLA for about a little under 20 years when this started, and it never occurred to me that I'd be doing this. It really was one of these experiences where I had an ah-ha moment, and then it was just so incredibly interesting to me that I couldn't stop.

And I do think that probably my physician colleagues were sort of scratching their head like, oh, you know, she had such a promising career, now she's just totally focused on animals. On the other hand, there are a lot of medical students and a lot of my colleagues who are getting interested.

Part of the challenge is helping physicians see that animal health is really relevant to human health and so if you're going to be a breast cancer expert, then you should know about press cancer and lions in tigers and English Springer Spaniels and if you're an adolescent medicine doctor who is dealing with, you know, adolescents who take risks, then you should know that adolescent male sea otters take a lot of risks and why that happens and why we see zebra finches do what they do and you should know about predator inspection among adolescent gazelles. And there's just a lot that is relevant to taking care of human patients in the animal literature.

GROSS: I want to thank you so much for talking with us.

NATTERSON-HOROWITZ: Oh, it's a pleasure.

GROSS: Dr. Barbara Natterson-Horowitz is a cardiologist at the UCLA Medical Center. She co-wrote the book "Zoobiquity," which has just been published in paperback. You can read an excerpt on our website freshair.npr.org. Transcript provided by NPR, Copyright NPR.